Before You Start

You dont just need modules and case. A bit of your budget needs to cover actually making the modular produce sounds. You can always just use the modules themselves, even a simple LFO or envelope generator with cycle/loop/repeat can produce patterns/rhythms etc. as CV/Gate/trigger signals.

There are dedicated sequencing modules. The simplest as far as instant results is probably a keyboard/trigger button/pressure pad/theremin/ribbon controller/whatever controller that produces CV signals. Just plug the thing in and press/wave/slide hands and fingers to make noises.

Probably the most versatile for the money is a MIDI to CV module. There's a range of options from the Doepfer A-190 that are pretty cheap through to polyphonic monsters that take some programming patience. These will of course require a MIDI source to drive them. If you have a MIDI controller/keyboard/etc. then just plug in and, configured appropriately, you're set. A hardware sequencer will be similar as far as setup goes, but you'll need a little knowledge of programming MIDI hardware. Grooveboxes like the Korg Electribes and Yamaha RM1x excel at these tasks. A computer running a MIDI sequencer or DAW with MIDI capability is great if you get on with software, but you'll need a MIDI interface or MIDI over USB cable. The same MIDI options apply to non-module MIDI to CV converters. These stand alone units tend to offer greater fuctionality but often cost more.

If you want to use a computer running a DAW, by far the best option of the money is probably something from the Expert Sleepers range. Dedicated conversion of the outputs of an interface into CV signals via a plugin for the DAW, a module that takes audio and S/PDIF in, and provides CV sockets.

Often people starting a modular are on a budget or limited by space. Therefore want to cram the best amount function from a given spend. here's some things to consider. You will want oscillators to make noises, but oscillators also can provide CV for other modules. Since you are likely to want as many sounds and functions as possible from a sound source, it's definitely worth looking for LFOs that go up to audio frequencies and VCOs that go down to useful CV frequencies. Likewise, resonant filters and some loopable EGs and slope/slews can be pushed to oscillate at audio frequencies. Those EGs and slopes/slews that cycle etc. are also good sources of sequencing/distortion and other unexpected functions. VCOs with waveshaping and other cool functions not only save having to buy extra modules with those controls, but if they go down to LFO speeds then you can get weird wave shapes for cool CVing. Many of the less vanilla modules have multiple outs and ins, gain, offset, attenuation etc, saving on having to buy mixers, mults and other utility modules. Sometimes this justifies the extra cost. It's worth considering your need for processing audio, CV or both when buying stuff like VCAs and mixers. Switchable to Lin or Log can really save space. Modules with multiple audio inputs and outputs, CV inputs and outputs and CV-able parameters are good since they allow you to really get into the ethos of modulr sythesis - crossmodulation, feedback loops, frequency, gate or other control dependent shapes and rhythms etc.

Expensive modules arent just about sound quality, many sounds are distorted or the inherent imperfections that analog brings. Function is often the real gain. Cheaper modules arent in anyway bad. Some Doepfer modules outsell everything else, these not only do a cool thing, but also do it better than some of the competition when it comes to CV options, switchable ranges and ease of use. Certain manufacturers or designs of module have a very specific character - for example, an Analog Systems RS-180 VCA or a Malekko/Wiard Borg 1 sound very distinctive when used in certain ways and this may be the true appeal of such modules. Don't go by module funtion, reputation, cost etc. alone. Think what you want to achieve then read up and listen to examples to judge what would suit your desires the best. with some exceptions of very rare or expensive gear, it's uncommon to be able to build a replica of a specific bit of gear for less money using modules. So basically, think first 'what do i want to do with the modular', second 'what allows this but gives options do do other stuff or expand further' and then choose solutions based on budget or space.

As well as modules, what else is required? Patch cables, cheap ones can really spoil the fun. Looseness, intermittent connections, etc. Are they long enough versus shorter ones will tangle less and be more convenient to trace routings, as well as not crowding your working space. A variety of coloured cables can help when your patches get complex. A way of hearing the output? Output modules, mixers, interfaces etc. could be necessary for your setup. Headphones may need a dedicated amplifier, mixers will need some amplifier, speakers or powered monitors or Hi-Fi system, etc. Studio monitors can handle the unexpected, speaker blowing pops, peaks, thumps, and other abuses with less likelihood of damage. They're built for raw, unmixed, unmastered peaky sounds. A well grounded surge protected socket for the power into the modular. A decent power conditioner or proper supply might be worth considering. A cheap multimeter can help you quickly check stuff like cables, sockets or fuses etc.